Implemented smooth scrolling using xinput2 in X11.

chrome/browser/ui/views/frame/browser_root_view.cc

Index: chrome/browser/ui/views/frame/browser_root_view.cc
diff --git a/chrome/browser/ui/views/frame/browser_root_view.cc b/chrome/browser/ui/views/frame/browser_root_view.cc
index 8eaba179f86a695221aa7829c3ef50b382a47018..7f0b5bd4672a5cade3d67330fe2051d07c6d335e 100644
--- a/chrome/browser/ui/views/frame/browser_root_view.cc
+++ b/chrome/browser/ui/views/frame/browser_root_view.cc
@@ -28,7 +28,9 @@ BrowserRootView::BrowserRootView(BrowserView* browser_view,
                                  views::Widget* widget)
     : views::internal::RootView(widget),
       browser_view_(browser_view),
-      forwarding_to_tab_strip_(false) { }
+      forwarding_to_tab_strip_(false),
+      scroll_amount_x_(0),
+      scroll_amount_y_(0) {}
 
 bool BrowserRootView::GetDropFormats(
       int* formats,
@@ -130,19 +132,35 @@ bool BrowserRootView::OnMouseWheel(const ui::MouseWheelEvent& event) {
     if (tabstrip()->Contains(hit_view) ||
         hittest == HTCAPTION ||
         hittest == HTTOP) {
-      int scroll_offset = abs(event.y_offset()) > abs(event.x_offset()) ?
-          event.y_offset() : event.x_offset();
+      scroll_amount_x_ += event.x_offset();
+      scroll_amount_y_ += event.y_offset();
+
+      // Number of integer scroll events that have passed in each direction
+      int whole_scroll_amount_x = round(
+          (double)scroll_amount_x_ / (double)ui::MouseWheelEvent::kWheelDelta);
+      int whole_scroll_amount_y = round(
+          (double)scroll_amount_y_ / (double)ui::MouseWheelEvent::kWheelDelta);

[sadrul, 2016/01/05 16:46:23]

Use std::lround() (like in https://codereview.chromium.org/1554253004/).

Use static_cast<double> instead of (double). (you need to cast just the num to
double I think)

[Will Shackleton, 2016/01/05 21:27:02]

Done.

+
+      scroll_amount_x_ -=
+          whole_scroll_amount_x * ui::MouseWheelEvent::kWheelDelta;
+      scroll_amount_y_ -=
+          whole_scroll_amount_y * ui::MouseWheelEvent::kWheelDelta;
+
+      // Count a scroll in either axis - summing the axes works for this.
+      int whole_scroll_offset = whole_scroll_amount_x + whole_scroll_amount_y;
+
       Browser* browser = browser_view_->browser();
       TabStripModel* model = browser->tab_strip_model();
       // Switch to the next tab only if not at the end of the tab-strip.
-      if (scroll_offset < 0 && model->active_index() + 1 < model->count()) {
+      if (whole_scroll_offset < 0 &&
+          model->active_index() + 1 < model->count()) {
         chrome::SelectNextTab(browser);
         return true;
       }
 
       // Switch to the previous tab only if not at the beginning of the
       // tab-strip.
-      if (scroll_offset > 0 && model->active_index() > 0) {
+      if (whole_scroll_offset > 0 && model->active_index() > 0) {
         chrome::SelectPreviousTab(browser);
         return true;
       }
@@ -151,6 +169,13 @@ bool BrowserRootView::OnMouseWheel(const ui::MouseWheelEvent& event) {
   return RootView::OnMouseWheel(event);
 }
 
+void BrowserRootView::OnMouseExited(const ui::MouseEvent& event) {
+  // Reset such that the tab switch always occurs halfway through a smooth
+  // scroll
+  scroll_amount_x_ = 0;
+  scroll_amount_y_ = 0;
+}
+
 void BrowserRootView::OnEventProcessingStarted(ui::Event* event) {
   if (event->IsGestureEvent()) {
     ui::GestureEvent* gesture_event = event->AsGestureEvent();